The Lesson - A Bridge On Guard Span's Protective Shield Called Best In The World

March 22, 1987|By Tom Scherberger

Haunted by the 1980 Sunshine Skyway bridge accident that killed 35 people, state officials quickly decided to spend whatever it might take to make sure that history never repeats itself.

It was a decision that will cost taxpayers $41 million -- more than it cost to build the original bridge in 1954. Engineers have designed a system of concrete buffers and electronic devices that, when completed next year, will make the Skyway the most protected bridge in the world.

The two main piers already are protected by four concrete ''dolphins'' that were built long before the bridge was completed. Each dolphin is 60 feet in diameter and cost $1 million to build. They are designed to fend off errant ships, as are 32 smaller dolphins now under construction. In addition, small rock islands will surround the two main piers. If a ship somehow gets past the dolphins, it will be grounded on the islands before it hits the piers.

A slew of high-technology gadgets also will boost bridge safety. They include an electronic guidance system to help harbor pilots ferry ships under the bridge during stormy weather, an electronic system to warn motorists of pending danger, closed-circuit television cameras to monitor traffic on the bridge, electronic sensors installed on the bridge piers to detect even the most minor collisions and a radio link between the harbor pilots and bridge- tenders.

Michael Knott, the engineer who designed the system, has emerged as one of the world's leading experts on bridge protection. His work has led to a pioneering computer software system to help analyze the risk of bridge disasters. And he is serving on an international panel studying the problem of unprotected bridges.

Bridge designers historically have worried about natural disasters that might knock down their structures. They would build bridges to withstand hurricanes, floods or tornadoes. But Knott has discovered that ship collisions are a much bigger threat than any natural disaster. His research turned up at least one major ship-bridge collision somewhere in the world annually in recent years.

''Most bridges in our country and in the world are not protected,'' said Knott, a soft-spoken, bearded engineer in the Tampa office of Greiner Engineering Sciences Inc.

Knott has turned a $1.4 million consulting contract into a personal crusade. He said that most bridges are disasters waiting to happen, yet few governments have done anything about them.

The Skyway, for example, had been hit 13 times before the Summit Venture finally knocked down a quarter-mile section of roadway. All but three of those collisions involved barges. None resulted in major damage or loss of life. At the time of the accident, an average of about two dozen vessels a day traveled beneath the Skyway. That number is expected to double by the year 2000.

The worldwide problem, Knott said, is as simple as dollars and cents. ''We build entire bridges for less money than it took to protect the new Skyway,'' he said. ''There are no cheap solutions. That's the problem.''

It took nine months just to figure out the likelihood of a ship hitting the Skyway. A study found that if the Skyway were unprotected one of its 12 main piers would be hit every 38 years. Yet engineers had designed the bridge to last at least 50 years.

Now, Knott estimates, with its protection system, a ship will collide with the bridge once every 427 years.

The concrete dolphins are sunk 30 feet into the bottom of the bay and rise 15 feet above the surface. They are designed to stop a ship, not sink it. ''In small collisions, ships will really just bounce off,'' Knott said.

He said he hopes that the Skyway's protection system will set the standard for future bridges and that existing bridges also will get some protection.

''This is a serious problem people better start looking out for,'' Knott said. ''How many people have got to get killed before we face up to it?''